ABSTRACT Relapse to drug seeking after abstinence is a major challenge in treating substance use disorder. Abstinent drug users remain at risk of relapse even after extended drug-free periods. Exposure to drug-associated cues or stress during abstinence can trigger intense craving and precipitate relapse. New and more effective anti-relapse interventions are critically needed, particularly for cocaine use disorder since no effective pharmacological intervention is available. We discovered that a nutritional supplement we developed for clinical use, as part of a nutritional approach for managing substance use disorder, had the benefit of being a potentially robust anti-relapse therapy. This supplement, SMAASH-C, contains a combination of vitamins, omega-3 fatty acids, and minerals, as well as tyrosine and other amino acids that are known to be depleted by chronic cocaine exposure. We originally learned of its potential therapeutic value through anecdotal reports from our patients of reduced drug craving, reduced stress and anxiety, and less frequent relapses. As a follow-up, we screened SMAASH-C in a rat model of relapse, and confirmed its potential efficacy as an anti-relapse intervention. Specifically, we found that 15-days of SMAASH-C treatment during abstinence, via a clinically relevant oral route (mixed in food), resulted in a 50% reduction in extinction and cue-induced cocaine-seeking as compared to control treatment (non-supplemented food). Notably, SMAASH-C did not affect body weight, food intake, or non-specific responding during the cocaine-seeking tests indicating its potential as a safe and selective intervention. In fact, results from toxicology analyses of a 12-week SMAASH-C treatment regime in saline and cocaine-withdrawn rats suggests that it offsets markers of cocaine-induced toxicity (e.g., oxidative stress, hepatic injury). The overall objective of this R21 application is to provide preclinical proof-of-concept data for the use of SMAASH-C as an effective, safe, and selective anti-cocaine relapse intervention. To do so, we will determine its efficacy at reducing cocaine-seeking following extended access self-administration and protracted abstinence, and in response to two of the most common triggers of craving and relapse in humans: drug-associated cues (Aim 1) and stress (Aim 2). Selectivity will be assessed by comparing effects on cocaine- versus sucrose-seeking. Both males and females will be included given literature highlighting the need for sex-specific interventions. As a first step toward understanding the mechanisms underlying its efficacy, we will examine markers of dopaminergic and glutamatergic signaling in the reward pathway following relapse testing using qPCR and Western Blot analysis. Our overall hypothesis is that SMAASH-C will robustly (>50%), selectively (no effect on sucrose-seeking), and dose-dependently decrease relapse vulnerability and associated neuroadaptations in both males and females. Our long-term goal is to bring SMAASH-C into clinical trials as a single or adjunct intervention for cocaine relapse. This application is a major step toward this goal since the results will provide the necessary preclinical proof-of-concept data.